JPH03250509A - Manufacture of superconducting oxide wire - Google Patents

Abstract

PURPOSE:To manufacture a superconducting oxide wire of dense crystallization, high crystal orientation and high critical current density by filling the power of a Bi group oxide superconductor into a metal sheath to be cold-worked and heat-treated respective ly under specified conditions. CONSTITUTION:The powder of a Bi group oxide superconductor is filled into a metal sheath to be cold-worked, heat-treated at a temperature not higher than 875 deg.C and subsequently cold-worked, then heat-treated at a temperature not lower than 870 deg.C and heat-treated again at a temperature not higher than 875 deg.C. As for manufacture of the Bi group oxide superconductor, such a component that never damages the characteristics of a Bi-Sr-Ca-Cu-O group composition may be optionally added to the composition. A low Tc phase Bi2Sr2CaCu2 group composition, for example, can give a high critical current density characteristic (Jc). The wire can be manufactured not only for general-purpose but also into a tape-shaped one or a multicore linear one. The primary, secondary and tertiary heat treatment causes crystal growth to the superconductor in the preferential direction while correcting the distortion of crystal grains of the superconductor, whereby an oxide superconducting wire of dense crystallization, high crystal orientation and high critical current density can be manufac tured.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing an oxide superconducting wire. More specifically, the present invention relates to a method for producing a Bi-based oxide superconducting wire having critical current characteristics that can be put to practical use and is useful for various superconducting magnets, power transmission cables, generators, etc.

(Conventional technology and its issues) Bi-based oxides are attracting attention as high-temperature oxide superconductors, and efforts are being made to make the Bi-based oxide superconductors thinner and to process them into wires and tape-shaped bodies. is being considered.

Already, Bi-based oxide superconductor powder has been filled into a silver sheath, processed into a wire or tape, and then subjected to orientation treatments such as sintering, rolling, and sintering. A method of manufacturing a conductive wire or a superconducting tape has also been proposed.

However, in the methods known so far, Bi
In the case of Bi-based oxide superconductors, the actual situation is that wires or tape-like bodies with a critical current density (Jc) that can be used in practical use cannot be obtained.6 Bi-based oxide superconductor anisotropy It is large and current flows easily in the a-b plane. Therefore, in order to obtain a high critical current density (Jc), it is necessary to make the structure dense and to achieve high orientation of the ab plane. In addition, during post-processing heat treatment, especially in multicore wires, there is a problem that reactions between the oxide superconductor and the sheath metal tend to occur, resulting in deterioration of characteristics, so countermeasures are needed in this regard.

This invention was made in view of the above-mentioned circumstances, and it overcomes the drawbacks of the conventional wire manufacturing method, achieves a dense structure and high orientation, has a high critical current density, and has a sheath metal. The object of the present invention is to provide a method for producing a high-performance Bii oxide superconductor wire that suppresses reactions with other materials.

(Means for Solving the Problems) This invention solves the above problems by packing Bi-based oxide superconductor powder into a metal sheath, cold working it, and heat-treating it at a temperature of 875°C or lower. After that, it is cold worked, then heat treated at a temperature of 870°C or higher, and then 875°C
Provided is a method for producing an oxide superconducting wire characterized by heat treatment at a temperature of 0.degree. C. or lower.

The Bi-based oxide superconductor targeted in the method of this invention has a B1-5r-Ca-Cu-0 system as its basic composition, and any components that do not impair its properties may be added. It can also include things.

In particular, among these compositions, in this invention, low Tc
It is noteworthy that it is possible to obtain a high current density characteristic (Jc) from a composition of the Bi Sr CaCu2 system, which is known as a phase.

Furthermore, the present invention includes wire rods of various shapes and structures. For example, tape-shaped bodies and multicore wires are also included. The method of the present invention for manufacturing these wires can be summarized as follows when explained in the order of its steps.

(1) Filling a metal sheath and cold working A raw material powder of an i-based oxide superconductor having a predetermined composition is filled into a metal sheath made of silver or the like, and initial cold working is performed. This processing can be performed by appropriate means such as a roll press.

In this step, it may be advantageous to use powder that has been heat-treated in advance as calcination or pre-sintering to a Bi-based oxide superconductor powder at a temperature of about 700 to 875°C, and then rapidly cooled to around room temperature. be. By using this powder, an oxide superconducting wire having a high critical temperature (Tc) can be obtained. For example, even with a superconductor having a low Tc phase, a wire with a level of about 90% can be obtained.

At this time, the rapid cooling to around room temperature is Preferably, the reaction is carried out at a rate of 300° C./hour or higher.

If it is slower than this, a decrease in the critical temperature may be observed.

This is presumably caused by changes in oxygen content.

) - Heat treatment and cold working Next, heat treatment is performed at a temperature of 875°C or less, and cold working is performed. This process allows crystal growth without melting the oxide phase,
The purpose is to achieve strong preferential orientation in the length direction by cold working such as rolling or wire drawing.

When the heat treatment temperature exceeds 875° C., the material becomes a semi-molten state before a strong preferential orientation is formed, and crystals grow in random directions, degrading superconducting properties.

In addition, in this heat-forming treatment, it is preferable to raise the temperature gradually or stepwise to a predetermined treatment temperature. This suppresses the reaction between the metal sheath and the oxide superconductor,
It is particularly effective in obtaining good characteristics in multicore wires and the like. If the temperature is raised rapidly, partial melting occurs at a relatively low temperature before phase formation and homogenization occur, and a reaction with the metal sheath occurs, which tends to deteriorate the properties.

It is preferable that the temperature be raised gradually or stepwise to a predetermined temperature over a period of at least 10 hours.If the temperature is lower than this, the effect of suppressing the reaction with the metal sheath will not be sufficient.

After completing the cold working to give the secondary heat treatment preferential direction, 870'C
Secondary heat treatment is performed at the above temperature. The purpose of this heat treatment is to bring the oxide phase into a semi-molten state and cause crystal growth along the preferred orientation.

Since melting does not occur below this temperature or is completely insufficient, crystal growth for high density and high orientation does not occur.

In this secondary heat treatment as well, for the same reason as (2) above, the temperature is raised gradually or stepwise to a predetermined temperature.
It is preferable to carry out the process for 0 hours or more.

3) For example, in the production of multicore wires, the temperature can be raised in stages such as 850°C x 20 hours, 870°C x 20 hours, and 880°C x 15 hours, and this process involves the reaction between the metal sheath and the superconductor. Extremely advantageous for suppression.

(4) Tertiary heat treatment Finally, tertiary heat treatment is performed at a temperature of 875° C. or lower to increase the degree of crystal order.

The purpose of this is to correct the distortion of crystal grains caused by the operations up to the secondary heat treatment and restore the order of the crystals.

Of course, in the method of the present invention as described above, there are no particular limitations on the means for heating, cold working, etc., and the equipment therefor. Furthermore, various aspects are possible regarding the details of the process. Examples will be shown below, and the manufacturing method of the present invention will be explained in detail.

Example I Raw material powders were mixed to have a composition of Bi:Sr:Ca:Cu=2:2:1:2, and calcined at 800°C for 15 hours and preheated at 850°C for 10 hours. ℃
After cooling to room temperature at a rate of 1/2 hour, it was packed in a silver sheath and processed into a tape. This was heat-treated at 850°C for 15 hours, then cold-rolled to reduce its thickness by half, and then subjected to semi-melting heat treatment at 880°C for 15 hours and 850°C for 15 hours.
A tertiary order recovery heat treatment was performed at 0° C. for 50 hours.

Critical temperature of the obtained wire: TC is 86, 4.2
Critical current density at a magnetic field of 30T: Jc is 70.
It was 0OOA/-. Also in 77 and J in OT
c was 5.00OA/aa.

Example 2 A powder having the same composition as in Example 1 was preheated at 800°C for 15 hours and at 850°C for 10 hours.
A tape-shaped body was prepared in exactly the same manner as in Example 1 by cooling at a rate of 0° C./hour. The Tc of this wire is 90, and the Jc in a magnetic field of 4.2 and 30T is 85,0OO
It was A/-. Also, Jc at 77 and OT is 3
It was 5,0OOA/-.

Example 3 Powder with the same composition as in Example 1 and subjected to the same preheat treatment was packed into a silver sheath and processed into a thin wire, then bundled and inserted into a silver pipe, and cold processed again to contain 330 cores. A multicore tape made of Bi-based oxide was created. This was heat treated at 800°C for 20 hours, at 830°C for 20 hours, and further at 850°C for 15 hours (sample A).
After heat treatment at 50°C for 15 hours, rolling was added, followed by further heat treatment at 880°C for 10 hours and at 850°C for 50 hours.
A wire rod was prepared by heat treatment for hours (sample B). The Tc of samples A and B was 86 and 78, respectively, and the Jc at 4.2 and 30T was 26.0O, respectively.
OA/- and 10,0OOA/alY.

Example 4 After processing a 330-core multi-core tape using the same raw materials and the same process as in Example 3, it was heated at 800°C for 20 hours and at 830°C.
After heat treatment at 850°C for 20 hours and 850°C for 15 hours, rolling was performed at 850°C for 20 hours and at 87°C for 20 hours.
Heat treatment at 0'CX for 20 hours, further heat treatment at 880°C for 10 hours, and order recovery heat treatment at 850°C for 50 hours were performed. T
c is 89 and Jc at 4.2 and 30T is 3
It was 7,0OOA/cd. Also, 77 and OT
Jc was 31,0OOA/-.

(Effects of the Invention) As explained in detail above, the manufacturing method of the present invention allows B to be densified and highly oriented, and has a high critical current density.
An i-based oxide superconducting wire is obtained.

Furthermore, since this method allows a reaction between the metal sheath and the superconductor to occur, deterioration of the special product is also suppressed.

Claims (4)

[Claims] (1) Bi-based oxide superconductor powder is packed in a metal sheath, cold worked, heat treated at a temperature of 875°C or lower, cold worked, then heat treated at a temperature of 870°C or higher,
A method for producing an oxide superconducting wire, further comprising heat-treating at a temperature of 875° C. or lower. (2) Manufacturing the oxide superconducting wire according to claim (1), wherein the raw material powder is heat treated at a temperature of 700 to 875°C, and then the powder is rapidly cooled to around room temperature at a rate of 300°C/hour or more and packed into a metal sheath. Law. (3) In the manufacturing method according to claim (1) or (2), the oxidation is performed after the initial heat treatment at a temperature of 875°C or lower is gradually or stepwise raised over at least 10 hours. Manufacturing method of superconducting wire. (4) In the manufacturing method according to claim (1), (2) or (3), the heat treatment at a temperature of 870°C or higher is performed after the temperature is gradually or stepwise raised over at least 10 hours. A manufacturing method for oxide superconducting wire.